Abstract
The mechanical properties of Ti-6Al-4V can be improved by microstructural control through the heat treatment in ${\alpha}+{\beta}$ region. The heat treatment was carried out with a variety of heat treatment temperatures and holding times to find the optimized heat treatment conditions and it was analyzed by linking the microstructural characteristics and mechanical properties. The part of ${\beta}$ phase with $10{\pm}2wt%$ vanadium was transformed into ${\alpha}^{{\prime}{\prime}}$ martensite phase after quenched, so the hardness and tensile properties were decreased below $900^{\circ}C$. The higher the heat treatment temperature is, the smaller is the vanadium-rich region, which leads to transformation into hcp ${\alpha}^{\prime}$ martensite above $900^{\circ}C$. The hardness and tensile properties were improved due to the hard ${\alpha}^{\prime}$ martensite. As the holding times were longer, the hardness and tensile properties decreased below $900^{\circ}C$ because of the softening effect by the grain growth. When varying the holding times above $900^{\circ}C$, the change of mechanical properties was slight because the softening effect of grain growth and the strengthening effect of ${\alpha}^{\prime}$ phase were counteractive. Therefore, the best conditions of heat treatment, which is in the range of $920{\sim}960^{\circ}C$, 40 min, WQ, can effectively improve the mechanical properties of Ti-6Al-4V.